Owner contribution
Found the perfect bag to carry the D700 with Sigma 150-500 attached: LowePro Flipside 300. Leaves plenty of room for accessories. It even has a clip on the front to carry a monopod/tripod.

The compact, lightweight design of the Flipside 300 backpack lets you carry your pro digital SLR without worry. The unique back compartment entry gives you safe, easy access to camera gear when you’re setting up plus extra security when you’re on the move. Outer storage panels keep digital accessories and personal items close at hand.
1 Pro DSLR with 300mm f/2.8 lens attached plus 1–3 additional lenses or flash units, 1 tripod, multi
Found the perfect bag to carry the D700 with Sigma 150-500 attached: LowePro Flipside 300. Leaves plenty of room for accessories. It even has a clip on the front to carry a monopod/tripod.
In my quest for the ultimate bag, I have purchased some great bags from Domke and Lowepro. Although I still have some of these bags and they have their place, I really am enjoying this new bag from Lowepro. I have had it for a week and I am very satisfied with my purchase. It's a great bag to safely carry a few lenses and accessories. I have been a big fan of the reviews on cambags.com and this is my first review. I LOVE this bag. I have photographed street events and sports and I always had to be conscious of who was behind me when wearing my backpack or shoulder bag. With the Flipside, I can relax quite a bit since the only things a thief would get to are the water bottle, snack bar, business cards, pens and a couple of old 512 cards that I keep as emergency backups. The bag is light. Even with the heavy lens listed above, the bag is both comfortable to wear and carry. I feel I can wear this bag longer than I can my other bags so far. The bag is of a slim design and comes with one long accessory pocket and a mesh pocket on the other side. The mesh pocket will fit a 16oz bottle and a couple of snack bars. You could probably fit a 20oz bottle too. The accessory pocket does an okay job. I was hoping to fit my Lumiquest ProMax but it is just too tight in this compartment. Just use it for the bare essentials; extra memory cards, lens brush, small pocket knife, business cards, writing pad and pens. It has key hook and mesh pocket but it gets hard to close with too many things added. Would be nicer if this was a little bigger. I love the fact that the bag opens from the side that is against your back. Not only is this great for security reasons, but it keeps you from getting dirty or wet when you have to put the bag back on your back after putting down to get to your gear. I photographed a garden for four hours last week and it was so cool to be able to just pick up the bag without constantly brushing off the debris. The zippers are nice and smooth and I found no problem getting quick access to my gear. The waist belt is thin which may only help a little in a long trek versus the wider belts on Classic Trekker and Mini Trekker. Haven't tried attaching a Slip-Lock item to it as it is so thin it may slip off when I put the bag down. I haven't tried it myself but you can actually swing the bag around and use it as a waist bag. As another reviewer stated, I would be hesitant to have my expensive equipment dangling from a thin waist belt with one small connector. The should straps have Slip-Lock loops on them. I have attached a memory card holder to one and may get a lens pouch for the other. I do wish that the loops were lower. However, the shoulder straps are wide enough for me. I am 5'10" It also has one big carrying handle to which I attached a ball-bungee cord. May use it to carry my flash bracket too. Inside the bag, there is a accessory bag which is Velcro to the top but can be removed to accommodate a longer lens. It has plenty of room for extra batteries, charger cleaning supplies, remote cord and the battery holder for the D300 grip with room to spare. The dividers are not as customizable as other Lowepro bags. The compartment doesn't have the felt part all around the inside of the bag. Because of the slimness of the bag, you essentially get 2 1/2 rows as oppose to the full three rows. I don't see this a problem for most as you can use the half space for a flash with an Omni-Bounce diffuser. I was also able to fit two flashes side by side when they are folded in their normal shooting position. The pictures show my setup if I was to shoot an event or sports game. Because of the size of the lenses, you can only fit two or three. I used two of the dividers under the 80-200 for added support. Also, the lens hoods for the 24-70 and 80-200 may not fit depending on the configuration, so I use a rubber hood instead which what I would use anyway when shooting sports. On top, I put the four piece filter case and can also fit a mini-tripod. The inner flap is pretty thin. I have the LumiQuest Pro System pieces without the wallet, a PhotoBert CheatSheet, a flat ND-Gradual filter and Grey/White Card with a Nikon D300 quick guide. The flap doesn't fold down all the way which makes it take a bit longer when you are accessing whatever lens or accessory you have in the lower part of the bag. My other setup that I tested was with the D300, Nikon 24-120 AF-D, Nikon 105 Micro, Nikon 50 1.8 AF-D, Sigma 10-20 lens and the SB-800 flash. Have also tested a portrait configuration with two Pocket Wizards, a couple of flashes and the 24-70 and 80-200 lens. Although you're still a big target if you got your camera out of the bag, I immediately felt more confident shooting in crowds and I don't feel I have to put my bag down on the sidelines because it gets too uncomfortable or heavy to wear. Overall, this is a great bag and I am really enjoying working out of it. If I had to change some things, it would be perhaps a small pouch on top for maps, gum or small LED flashlight. Would also like to see a slightly bigger accessory side pocket, Velcro in the inner accessory pouch for better organization or two smaller pouches to have the choice of placement or removal. Dividers that gave more options. Lower SlipLock loops. I think that for most of my uses, this will be my main bag. Would only trade it for a newer model of Flipside. Would highly recommend this bag if you're looking for the minimalist approach to photography. My brother in law is getting one for Christmas Well done Lowepro.
Confidence about security. Light and easy to carry.
Love/Hate the Side pouch. SlipLock loops too high.
I normally prefer shoulder bags (Domke), but have recently been looking for a "hands-free" solution ie: a backpack and I've found this one very useful. Here's where I'm coming from: I was initially interested in the original Lowepro Slingshot, but when I tried one loaded it just didn't feel right. I don't like squeezing equipment into my bags too tightly but I needed something to carry a D200+ grip plus two of my main lenses (17-55, 70-200vr) with either one attached. The Slingshot 200 was too small, and the 300 felt very ungainly and the single shoulder strap just wasn't for me. So I tried this Flipside 300. Shape / ergonomics: I'm 6ft 1". I have found when choosing backpacks for a small/moderate amount of equipment they tend to look a little strange, a small, fat bag perched up between your shoulder blades with a tendency to flop from side to side unless you use all the harnesses all the time. Larger backpacks of course extend further down your back and offer better balance in my opinion, but I don't want to weigh myself down with that much stuff, or carry a large half empty bag. The Flipside 300 is good in this respect as it is comparatively thin and tall. I have no problem with the fit and it is very comfortable. It has adjustable sternum and waist straps. If I was being picky I would say the straps would benefit from a little extra padding, a wider waist belt (see below) and the whole rig would fit *me* better if it was a few inches taller still but on the whole, no complaints at all. The flipside design Very good idea and reduces paranoia when in large crowds such as in cities. Practically impossible for anyone to gain access to the main compartment without you realising. The nice thing is, and it not often clear in the marketing material - it can be used similarly to a Slingshot or other such quick access pack. With the waist belt on, slip your arms out and twist the whole bag around your waist and the bag ends up on your front, still attached and with the access panel to the main compartment facing you. I wouldn't go jumping around with the bag attached like this, but it's certainly sturdy enough to support the weight of all the items shown in the pic while accessing / swapping lenses etc. With a bit of practice it can all be done very quickly (even while walking) without the need of putting the bag down on the floor. Again, if I was being picky I would like slightly wider / more padded / more substantial waist belt to improve this feature further, possibly with a double clip to eliminate the risk should the single connector break, of dropping all your stuff 100metres down the side of a mountain and into a crocodile infested river. With either lens attached and some jiggery-pokery with the dividers they all fit, it's a bit on the tight side due to all 3 large lens hoods but one of these could be removed and put in the extra compartment (6) if required. This compartment (6) is also big enough to fit a small/medium size prime lens, filters, batteries etc. I leave some of the velcro un-hooked (5) for breathing space. Only certain sections of the walls have velcro on them, so it's not quite as customisable as it might be. If I removed one of the above lenses I could fit a flash unit in the (currently empty) side compartment on the left. Exterior compartments / other bits One exterior compartment is thin and zippered, for pens and business cards, maybe a mobile phone but to be honest I don't use it. The other is an expandable mesh pocket ideal for a hat / gloves / drink. Good, strong carry handle on the top of the backpack and the whole thing stands up nicely. My only real gripe with Lowepro bags in general is how they look. I'd like this bag even more if it was finished in similar canvas to a Domke or NG bag in more earthy colours like olive or tan, but it is what it is and that's just my preference. I suppose if it was canvas it might lose some of it's water resistance (which I can't comment on because I've only used it in light rain.
Great design. Economical use of space, holds quite a lot without being huge. Better, longer, thinner shape than many small/medium sized packs. Quick access to user is a nice bonus. Flipside security feature is a good idea.
None serious enough to prevent me recommending the bag. Straps/belt could be a little more padded, better (personal) but could compromise water resistance.
The Lowepro Flipside 300 is a very solid backpack, all the gear goes nicely in and it feels very good to carry on your back even fully loaded. It has a tripod holder on the other side, my Manfrotto190XPRO tripod with the 486RC2 head fits there also.
Having a hard time finding info on the Lowepro Flipside 300? There is a dearth of information on the net, I think I may be the first to review this new photo backpack. I have seen these items on the B&H Photo and Adorama websites for several months now, recently the stores started showing that they were available. The bag has a lot of the features that I was looking for in a backpack. It is compact and lightweight. I also like the fact that the bag opens from the back panel. This is comforting in a crowded setting, aside from the side mounted accessory pouch, all the zippers are on the back panel. The straps are very comfortable and the there is a comfortable mesh material to keep the air moving. The accessory pouch inside the bag is removable. If you were not interested in carrying your charger or could tuck it along the side of the bag, you could easily install dividing material into the void and store additional lenses. Overall, I am very happy with the bag, and I look forward to taking it into the field.
Lots of Room Cheap (Under $75) Secure Design Comfortable Compact
Not as Red as I anticipated. More maroon than red. The accessory pocket on the side of the bag could be more roomy.
A very compact backpack, I'm sure it's bigger on the inside than on the outside. Will hold an amazing amount of gear, considering how small it is. Build quality is up to LowePro Standards: Top notch, excellent padding, smooth zippers etc. Due to the unique back-opening design this bag looks very "clean" - And certainly not like a camera bag.
Compact, comfortable, rugged, Holds my "walk-around kit" very comfortably.
No AW cover... Come on, LowePro - Give us the Flipside 500AW!